This invention relates to an improved catalyst for the conversion of hydrocarbons, and more specifically for the catalytic reforming of gasoline-range hydrocarbons.
The subject of the present invention is a novel dual-function catalyst, characterized by a multimetallic, multigradient combination of three or more metal components in specified concentrations on the finished catalyst, and its use in hydrocarbon conversion. Catalysts having both a hydrogenation-dehydrogenation function and a cracking function are used widely in many applications, particularly in the petroleum and petrochemical industry, to accelerate a wide spectrum of hydrocarbon-conversion reactions. The cracking function generally relates to an acid-action material of the porous, adsorptive, refractory-oxide type which is typically utilized as the support or carrier for a heavy-metal component, such as the Group VIII (IUPAC 8-10) metals, which primarily contribute the hydrogenation-dehydrogenation function. Other metals in combined or elemental form can influence one or both of the cracking and hydrogenation-dehydrogenation functions.
In another aspect, the present invention comprehends improved processes that emanate from the use of the novel catalyst. These dual-function catalysts are used to accelerate a wide variety of hydrocarbon-conversion reactions such as dehydrogenation, hydrogenation, hydrocracking, hydrogenolysis, isomerization, desulfurization, cyclization, alkylation, polymerization, cracking, and hydroisomerization. In a specific aspect, an improved reforming process utilizes the subject catalyst to increase selectivity to gasoline and aromatics products.
Catalytic reforming involves a number of competing processes or reaction sequences. These include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, dehydrocyclization of an acyclic hydrocarbon to aromatics, hydrocracking of paraffins to light products boiling outside the gasoline range, dealkylation of alkylbenzenes and isomerization of paraffins. Some of the reactions occurring during reforming, such as hydrocracking which produces light paraffin gases, have a deleterious effect on the yield of products boiling in the gasoline range. Process improvements in catalytic reforming thus are targeted toward enhancing those reactions effecting a higher yield of the gasoline fraction at a given octane number.
It is of critical importance that a dual-function catalyst exhibit the capability both to initially perform its specified functions efficiently and to perform them satisfactorily for prolonged periods of time. The parameters used in the art to measure how well a particular catalyst performs its intended functions in a particular hydrocarbon reaction environment are activity, selectivity and stability. In a reforming environment, these parameters are defined as follows:
(1) Activity is a measure of the ability of the catalyst to convert hydrocarbon reactants to products at a designated severity level, with severity level representing a combination of reaction conditions: temperature, pressure, contact time, and hydrogen partial pressure. Activity typically is designated as the octane number of the pentanes and heavier (xe2x80x9cC5+xe2x80x9d) product stream from a given feedstock at a given severity level, or conversely as the temperature required to achieve a given octane number.
(2) Selectivity refers to the percentage yield of petrochemical aromatics or C5+ gasoline product from a given feedstock at a particular activity level.
(3) Stability refers to the rate of change of activity or selectivity per unit of time or of feedstock processed. Activity stability generally is measured as the rate of change of operating temperature per unit of time or of feedstock to achieve a given C5+ product octane, with a lower rate of temperature change corresponding to better activity stability, since catalytic reforming units typically operate at relatively constant product octane. Selectivity stability is measured as the rate of decrease of C5+ product or aromatics yield per unit of time or of feedstock.
Programs to improve performance of reforming catalysts are being stimulated by the reformulation of gasoline, following upon widespread removal of lead antiknock additive, in order to reduce harmful vehicle emissions. Gasoline-upgrading processes such as catalytic reforming must operate at higher efficiency with greater flexibility in order to meet these changing requirements. Catalyst selectivity is becoming ever more important to tailor gasoline components to these needs while avoiding losses to lower-value products. The major problem facing workers in this area of the art, therefore, is to develop more selective catalysts while maintaining effective catalyst activity and stability.
The art teaches a variety of multimetallic catalysts for the catalytic reforming of naphtha feedstocks. Most of these comprise combinations of platinum-group metals with rhenium and/or Group IVA (IUPAC 14) metals.
U.S. Pat. No. 3,915,845 (Antos) discloses hydrocarbon conversion with a catalyst comprising a platinum-group metal, Group IVA metal, halogen and lanthanide in an atomic ratio to platinum-group metal of 0.1 to 1.25. The preferred lanthanides are lanthanum, cerium, and especially neodymium which was exemplified in Antos. U.S. Pat. No. 4,039,477 (Engelhard et al.) discloses a catalyst for the catalytic hydrotreatment of hydrocarbons comprising a refractory metal oxide, platinum-group metal, tin and at least one metal from yttrium, thorium, uranium, praseodymium, cerium, lanthanum, neodymium, samarium, dysprosium and gadolinium with favorable results being observed at relatively low ratios of the latter metals to platinum. U.S. Pat. No. 5,665,223 (Bogdan) teaches a catalytic composite comprising a refractory inorganic oxide, Group IVA (IUPAC 14) metal, platinum-group metal and europium wherein the atomic ratio of europium to platinum-group metal is at least about 1.3.
Moreover, U.S. Pat. No. 5,102,850 (Sanchez) discloses cerium dioxide and a catalytically effective amount of platinum, which is impregnated in a radial gradient on an automotive exhaust catalyst. This oxidized catalyst teaches a dual gradient of both platinum and cerium, which is unlike the present invention having uniform platinum and which is used in a different catalytic process.
It is an object of the invention to provide a novel catalyst for hydrocarbon conversion. A corollary object of the invention is to provide a reforming process having improved activity and selectivity for the production of gasoline and/or aromatics.
The invention originates from the discovery that a catalyst containing platinum, tin and cerium on chlorided alumina shows a favorable ratio of aromatization to cracking in a reforming reaction.
A broad embodiment of the present invention is a catalyst comprising a refractory inorganic oxide and a multimetallic, multigradient metal component comprising a platinum-group metal component, a Group IVA (IUPAC 14) metal component, and a surface-layer lanthanide-series metal component. The platinum-group-metal generally is present in the catalyst in an amount of about 0.01 to 2 mass-% on an elemental basis of component, the Group IVA (IUPAC 14) metal component in an amount of about 0.01 to 5 mass-% on an elemental basis, and the surface-layer lanthanide-series-metal component in an amount of about 0.05 to 5 mass-% on an elemental basis. The atomic ratio of the lanthanide metal to platinum-group metal preferably is at least about 1.5, more preferably at least about 2. The catalyst optimally also comprises a halogen, especially chlorine. In preferred embodiments the refractory inorganic oxide is alumina, the platinum-group metal is platinum, the Group IVA (IUPAC 14) metal is tin, and the lanthanide-series metal is cerium. A highly preferred catalyst consists essentially of platinum, tin and cerium on a halogenated alumina support.
In another aspect, the invention is a process for the conversion of a hydrocarbon feedstock to obtain an aromatics-enhanced product utilizing a catalyst comprising a refractory inorganic oxide and a multimetallic, multigradient metal component comprising a platinum-group metal component, a Group IVA (IUPAC 14) metal component, and a surface-layer lanthanide-series metal component. Preferably the hydrocarbon conversion is catalytic reforming of a naphtha feedstock, utilizing the catalyst of the invention to increase the yield of gasoline and/or aromatics in the product.
These as well as other objects and embodiments will become evident from the following more detailed description of the present invention.